An electronically controlled household sewing machine, which is able to prepare sewing patterns whose width exceeds the normal width of the patterns stored, has become known from German Offenlegungsschrift DE-OS 40,27,364. These pattern combinations are prepared by a combination of individual sewing patterns with individual stitches, at least some of which can be prepared at right angles to the direction of sewing of the individual pattern. Even though freely programmable individual patterns can be prepared with this machine, the coordinates of every individual stitch must be entered by hand into the program memory during programming.
In the area of industrial machines, embroidery machines have been combined with personal computers. Various programming devices have been developed here in order to develop the coordinate values of the touchdown sites of an embroidery pattern. In these programming devices, the coordinate values, which form the desired sequence of touchdown sites of the needle in a workpiece, are entered by the operator by hand directly into a memory device for each stitch position, and entry is possible via a screen display unit.
To simplify entry, a device (West German Offenlegungsschrift No. DE-OS 32,32,842 corresponding to U.S. Pat. No. 4,444,135), in which only the coordinates of the two end points of a straight line or of an arc section are to be entered, rather than having to enter every individual pair of coordinate values by hand, has become known as well. The control device will subsequently automatically compute the coordinates of the missing touchdown points of the needle, and insert these between the end points of the curve section.
The said programming device is used in a sewing machine which is equipped with a fabric frame that is freely movable in the direction of the X and Y coordinates. The fabric frame is driven by stepping motors during the time during which the needle has been withdrawn from the fabric. Even though the duration of movement of the fabric frame is consequently limited, the magnitude of the movement in the two coordinate directions can be freely selected, insofar as this is permitted by the free mobility of the frame during the predetermined time.
It is not possible to apply the prior-art measure to a sewing machine, in which the fabric to be sewn is transported by a feed dog extending through slots in a needle plate, because only rather minimal fabric feed movements of the feed dog in the two coordinate directions can be performed by stitch formation cycles due to the dimensions of the slots being limited because of the sewing technology.
For this reason, satisfactory programming of the intermediate stitches is not possible with the prior-art solution in the case of a straight seam. Entering the consecutive stitches manually is also almost impossible because of the complicated relationships to be taken into account.